The proper operation of a hospital's emergency power supply system (EPSS) is critical for seamless life-supporting operations. In the event of an interruption in the hospital's main feed from their utility, the EPSS provides an alternative energy source that maintains operation of all the critical (and many non-critical) loads. Loss of the EPSS in life-supporting systems is more than a mere inconvenience; it can be harmful or even deadly to the patients and adversely affect ongoing tests and procedures.
To this end, the National Fire Protection Association (NFPA) developed standard NFPA 110, titled “Standard for Emergency and Standby Power Systems,” which covers “performance requirements for emergency and standby power systems providing an alternate source of electrical power to loads in buildings and facilities in the event that the primary power source fails.” The scope of NFPA 110 includes installation, maintenance, operation, and testing requirements as they pertain to the performance of the EPSS.
The NFPA 110 lists many requirements for the installation, maintenance, operation, and testing of EPSSs, which directly affect three primary components of the EPSS: the emergency power supply (EPS), the automatic transfer switches (ATSs), and the protective devices.
Electrical systems in developed countries are typically comprised of large interconnected networks of conductors (called grids) to distribute energy from energy sources to loads. These grids have considerable redundancy, protection schemes, and electrical inertia that typically allow them to ride through faults, load fluctuations, and other transitory electrical system events with minimal adverse effects.
However, an EPSS operates as an islanded electrical system when the preferred electrical source is removed (i.e., when the facility is operating independently from the utility grid). In the event the preferred source is lost, EPSSs will transfer the load to the alternate (or backup) source via an automatic throw-over switch (ATS). An open-transition switching scheme is may be used to ensure that the two sources are completely isolated from each other to eliminate the risk of back-feeding a fault. Hospitals are a prime example of an energy consumer who intentionally islands (isolates) part or all of their electrical system to serve emergency loads.
What is needed is an effective way of predicting or projecting the instability of the system frequency in an islanded electrical system or notifying the end-user of a potential instability issue based on the load's operational behavior before the instability condition occurs, and ameliorating or eliminating the conditions or circumstances that cause such instability to occur. The present disclosure is directed to satisfying these and other needs.